I have always been fascinated by Stirling engines, and I must confess that (like hydraulic rams) no matter how many times I read the explanations of how they work, I still don’t have a clue.

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3 Responses to “Segway Inventor Dean Kamen Thinks His New Stirling Engine Will Get You Off the Grid for Under $10K”

The Stirling engine is an old design for a steam engine that didn’t work particularly well. You would shoot steam into a cylinder and move a piston. Then inject water to cool the steam, bringing the piston back. Watt (and others) said, “screw this” and just vented out the spent steam, using live steam to move the piston back (either double-acting or via another piston). That way you could scale up the engine as needed by just providing more steam. But in a closed system with a volatile material, a small amount of heat can move the piston as you alternate heating and cooling the sides. Put a magnet in the piston and a coil outside and a small amount of energy can generate electricity. Works well as a small engine, but doesn’t scale up well.

The Stirling engine worked well enough, but it was more expensive than the Watt engines, so it fell into disuse. However, the problems were more of the materials available – it was hard to get helium in 1814, for example. One of the biggest issues with the Stirling engine was the ‘heat regenerator’ – a device which helped port heat from the gas cooling in the ‘cool’ side to the ‘hot’ side, which helped in the efficiency. I believe Kamen’s contribution is to use modern materials to trap considerably more of this energy, boosting efficiency. The use of materials like ceramics for the piston and sides is another.

The beauty of any external combustion engine is you can theoretically burn anything, from oil to cow dung, to produce energy, so if your propane truck didn’t make it out to the farm, you could burn old corn cobs, hay, whatever to make electricity. Also, external combustion, because you have plenty of oxygen, usually only produces CO2 and H2O when burned. Kamen says his 10 kW unit would be too expensive for an individual home, but I know five homes on the wrong side of the road in Georgetown, Ontario, (about 45 minutes from Toronto) that were out of power for over 2 weeks last Christmas because of an ice storm. I’m sure those five homes would gladly split the cost to have this unit provide their power reliably. Down at my cottage in rural Quebec, no one has air conditioning, and most use propane tanks to heat their water and power their stoves, so again, a 10 kW unit would be perfect for our lane, powering 10 homes through the ubiquitous winter outages.